This invention relates to a printing device and more particularly, to a printing device of the line printer type which is compact and less expensive, which can effect printing at a high speed and which includes means for prevention of superimposed printing.
There have been proposed and practically employed a great variety of printing devices and one typical prior art printing device generally comprises a rocking member pivoted at one end to a shaft, magnet means for normally attracting and maintaining the rocking member inoperative, a spring anchored to the rocking member for acting to bias the rocking member away from the magnet means when the device is operated for printing, a trigger hammer pivoted to the other end of the rocking member and have a striking portion, a second spring anchored to the striking portion of the trigger hammer for normally biasing the trigger hammer to its inoperative position and a continuously rotating pawled wheel having a pawl for engaging and disengaging from the trigger hammer whereby when the magnet means is excited, the trigger hammer pivots to a position in which the trigger hammer lies within the rotation locus of the pawled wheel to engage or strike against the pawl of the pawled wheel so as to effect a printing operation. Thus, in the prior art printing device referred to above, since the magnet means is adapted to attract the rocking member thereto against the force of the spring which normally biases the rocking member away from the magnet means, the magnet means is required to have a substantially high magnetic force to attract the rocking member thereto against the force of the spring. Therefore, the magnetic means is inevitably massive and expensive. And since the magnetic means attracts the rocking member thereto, against the force of the spring which normally biases the rocking member away from the magnetic means, it requires a rather long time for attracting the rocking member which results in a slow printing operation. Furthermore, as long as the magnetic means continues to maintain its excited condition, since the trigger hammer lies in the rotation locus of the pawled wheel rotating continuously at a high speed even after one printing operation has been completed, the trigger hammer may repeatedly have delivered thereto a striking force by the rotating pawled wheel resulting in superimposed printing. The superimposed printing fails to provide clearcut printing.